The oogenetic period is applied to the time a primordial germ cell (gonocyte) ceases mitosis and enters into a series of meiotic prophases that culminates in the diplotene stage. It is during this period that one witnesses one of the outstanding, and yet unexplained puzzles of embryology: How a stem cell becomes a committed cell. The period that follows is especially important for the follicle and this period is called folliculogenesis. In an analysis of mammalian oogenesis, one cannot investigate the oocyte without studying the companion multifunctional granulosa cell and associated structures, i.e. basement membrane, vascularized theca interna, and the non-vascularized theca externa. Thus in a sense, mammalian oogenesis becomes a study of the ontogeny of the highly, hormonally integrated, Graafian follicle. The objective of this research proposal is to learn some of the basic, fundamental aspects of the dynamic morphology of mammalian oogenesis and folliculogenesis. Special attention will be given to the onset or initiation and maintenance of meiosis I, surface characteristics of the plasma membrane of the granulosa cell that accompany its differentiation by use of plant lectins, and the selective permeability of the basement membrane as it relates to the maintenance of the unique microenvironment of the developing Graafian follicle, under both normal and experimental conditions. The proposed experiments will utilize in vivo and in vitro techniques (tissue and organ culture), electron probe microanalysis, freeze fracture, transmission and scanning electron microscopy, fluoresceine and ferritin conjugated lectins as membrane probes, radioimmunoassay, and cytological procedures. The expected fundamental data will be integrated with that obtained about the reproductive process in general through other biological disciplines.